Field
Embodiments of the present disclosure generally relate to methods and apparatus for thermally processing a substrate.
Description of the Related Art
Substrate processing systems are used to fabricate semiconductor logic and memory devices, flat panel displays, CD ROMs, and other devices. During processing, such substrates may be subjected to chemical vapor deposition (CVD) and rapid thermal processes (RTP); RTP processes include, for example, rapid thermal annealing (RTA), rapid thermal cleaning (RTC), rapid thermal CVD (RTCVD), rapid thermal oxidation (RTO), and rapid thermal nitridation (RTN). RTP systems usually include a heating lamps which radiatively heat the substrate through a light-transmissive window. RTP systems may also include other optical elements, such as an optically reflective surface opposing of the substrate surface and optical detectors for measuring the temperature of the substrate during processing.
Layers of doped glass, such as borophosphosilicate glass (BPSG) or phosphosilicate glass (PSG), are used extensively in pre-metal dielectric (PMD) layers in logic and memory devices. Doped glass layers are typically deposited onto a substrate in a CVD system and are subsequently heated to a high temperature in an RTP chamber or a furnace. In one heating process, doped glass is densified by heating the doped glass to a temperature of 700-800° C. in an RTP chamber. Heating the doped glass reduces the porosity of the layer, relieves stress in the film, drives off residual impurities left from CVD deposition, stabilizes the dopants against atmospheric instability, and activates the gettering capability of the phosphorous oxides (POx) in the film for trapping alkali ions. BPSG can be heated to higher temperatures, such as 850-950° C., to decrease the viscosity of the BPSG and cause macroscopically visible flow (reflow) that planarizes the BPSG surface and enables the BPSG to fill surface features of underlying layers.
Further, ion implantation is a preferred method for introduction of chemical impurities into semiconductor substrates to form the pn junctions necessary for field effect or bipolar transistor fabrication. Such impurities include p-type dopants such as boron (B), aluminum (Al), gallium (Ga), beryllium (Be), magnesium (Mg), and zinc (Zn) and N-type dopants such as phosphorus (P), arsenic (As), antimony (Sb), bismuth (Bi), selenium (Se), and tellurium (Te). Ion implantation of chemical impurities disrupts the crystallinity of the semiconductor substrate over the range of the implant. At low implant energies, relatively little damage occurs to the substrate. However, the implanted dopants will not come to rest on electrically active sites in the substrate. Therefore, an “anneal” is required to restore the crystallinity of the substrate and drive the implanted dopants onto electrically active crystal sites. As used herein, “annealing” refers to the thermal process of raising the temperature of an electrically inactive region of a substrate from an ambient temperature to a maximum temperature for a specified time and cooling to ambient temperatures for the purpose of creating electrically active regions in a device. The result of such annealing and/or the annealing process is sometimes also referred to as “implant annealing,” “activation annealing,” or “activation.” Thermal processes such as rapid thermal processing (RTP) and spike annealing are the main dopant activation methods.
FIG. 1 is a schematic sectional view of a processing chamber 100 of a conventional process chamber design. The processing chamber 100 includes a chamber body 102 defining a processing volume 104. A window 106 is formed on a bottom side of the chamber body 102. A radiant energy source 108 is disposed below the window 106. The radiant energy source 108 is configured to direct radiant energy from the lamps towards the processing volume 104. A reflection plate 110 is disposed on an upper wall 112 of the chamber body 102 inside the processing volume 104. A plurality of sensors 126 may be positioned over the upper wall 112 to detect temperatures in the processing volume 104 through sensor ports 124 formed in the reflection plate 110 and the upper wall 112.
The processing chamber 100 includes a lift assembly 128 configured to vertically move and rotate a rotor 114 disposed in the processing volume 104. A supporting ring 116 is disposed on the rotor 114. An edge ring 118 is supported by the supporting ring 116. A substrate 122 is supported by the edge ring 118 during processing. The edge ring 118 and the substrate 122 are positioned above the radiant energy source 108 so that the radiant energy source 108 can heat both the substrate 122 and the edge ring 118.
During processing, the radiant energy source 108 is configured to rapidly heat the substrate 122 positioned on the edge ring 118, while the edge ring 118 heats an edge region of the substrate 122 by conduction through direct contact. The process of heating the substrate 122 causes one or more layers on or within the substrate to outgas (see arrows “A” and “B”). The material that outgases from the substrate will typically deposit on the colder walls, such as the reflector plate 110 disposed in the chamber. Moreover, semiconductor devices are typically formed on a device surface 122A of the substrate (e.g., top surface in FIG. 1), or device side of the substrate. Therefore, typically, during processing the amount of material that is outgassed from the surface of the substrate is typically greater from the device surface side (see arrows A) versus the non-device surface side (see arrows B) of the substrate. As the amount of outgassed material deposits on the surface of the reflector plate 110 the optical characteristics (e.g., reflectivity) of the surface change with time, which causes an undesirable drift in the processing temperatures of the substrates 122 processed in the process volume 104 of the conventional process chamber 100 over time. Moreover, the outgassed material will also deposit on the components (e.g., sensors 126) used to measure and control the temperature of the substrate during processing. The deposited material will thus affect the temperature measurements and the conventional system's ability to control the thermal processes performed in the processing volume 104.
The outgassed impurities may include dopant materials, a material derived from the dopant material, a material disposed in a layer formed on the surface 122A of the substrate 122. For example, boron oxides (BOx) and phosphorous oxides (POx) have high vapor pressures and are produced from the surface 122A when BPSG and PSG layers disposed thereon are heated to high temperatures.
This deposition created by the outgassing process interferes with the temperature pyrometer readings and with the radiation distribution fields on the substrate, which in turn affects the processing temperature at which the substrate is annealed. Deposition of the outgassed impurities may also cause unwanted particles to deposit on the substrate and may also generate slip lines on the substrate. Depending on the chemical composition of the deposits, the chamber must be taken offline for a “wet clean” process after about 200 to 300 substrates are processed. The wet clean process requires manual intervention to clean the deposited material from the chamber walls and from the reflector plate, which may be labor intensive requiring the chamber to be offline for about four hours.
Therefore, there exists a need for a method and apparatus that minimizes the amount of deposits on reflector and chamber walls to increase the mean substrates (wafers) between cleans (MWBC) and can also improve the thermal processing environment to improve the RTP process results. There is also a need for an improved thermal processing chamber design that reduces the effect that deposits generated by an outgassed material will have on the RTP process.